1. Field of the Invention
This invention relates generally to a cooling apparatus, with one exemplary embodiment being a cooling apparatus for cooling a heating electronic component of a central processing unit (hereinafter referred to as CPU) or the like arranged inside a casing, by circulating a refrigerant therethrough.
2. Description of the Related Art
The recent very rapid increase in the processing speed of computers has increased the clock frequency of a CPU, compared with computers in the past. As a result, the calorific value of the CPU increases and the cooling capability of air cooling by a heat sink as in a conventional technique is insufficient. Therefore, a highly efficient high-output cooling apparatus is required. Thus, as such a cooling apparatus, a cooling apparatus for cooling a board with a heating component mounted thereon by circulating a refrigerant therethrough is known, as disclosed in the Japanese Publication of Unexamined Patent Application No. H5-264139 and the Japanese Publication of Unexamined Patent Application No. H8-32263.
Such a conventional cooling apparatus for electronic equipment for cooling by circulating a refrigerant will now be described. The term xe2x80x9celectronic equipmentxe2x80x9d in this specification includes, but is not limited to, a device which loads a program to its CPU or the like and performs arithmetic processing, for example, a portable small device such as a notebook model personal computer, and/or a device having a heating element which heats when it is electrified. A conventional first cooling apparatus is shown in FIG. 8. FIG. 8 is a structural view of the first cooling apparatus for electronic equipment. In FIG. 8, 100 represents a casing, 101 represents a heating component, 102 represents a board with the heating component 101 mounted thereon, 103 represents a cooler for performing heat exchange between the heating component 101 and a refrigerant and thus cooling the heating component 101, 104 represents a radiator for removing the heat from the refrigerant, 105 represents a pump for circulating the refrigerant, 106 represents piping for connecting these elements, and 107 represents a fan for air-cooling the radiator 104.
The operation of this conventional first cooling apparatus will now be described. The refrigerant ejected from the pump 105 passes through the piping 106 and is fed to the cooler 103. There, as the refrigerant takes up the heat of the heating component 101, its temperature rises and the refrigerant is fed to the radiator 104. As the refrigerant is cooled by forced air cooling by the fan 107, its temperature is lowered and the refrigerant is fed back to the pump 105. This procedure is repeated. In this manner, the conventional cooling apparatus is adapted for cooling by circulating the refrigerant and thus removing the heat from the heating component 101.
A second conventional cooling apparatus for electronic equipment is disclosed in the Japanese Publication of Unexamined Patent Application No.H7-142886. This apparatus is schematically shown in FIG. 9. This second cooling apparatus is adapted for efficiently carrying generated heat of a heating member to a metallic casing wall as a radiator part and thus cooling the heating member when the heating member is mounted within a narrow casing. In FIG. 9, 108 represents a wiring board of an electronic equipment, 109 represents a keyboard, 110 represents a semiconductor heating element, 111 represents a disk device, 112 represents a display device, 113 represents a heat-receiving header for performing heat exchange with the semiconductor heating element 110, 114 represents radiation header for radiation, 115 represents a flexible tube, and 116 represents a metallic casing of the electronic equipment.
In this second cooling apparatus, the semiconductor heating element 110 as a heating member and the metallic casing 116 are thermally connected with each other by a heat carrying device of a flexible structure. This heat carrying device is constituted by the flat heat-receiving header 113 mounted on the semiconductor heating element 110 and having a liquid flow path, the radiation header 114 having a liquid flow path and being in contact with the wall of the metallic casing 116, and the flexible tube 115 connecting these headers. The heat carrying device is adapted for driving or circulating a liquid which is sealed therein, between the heat-receiving header 113 and the radiation header 114 by a liquid driving mechanism provided inside the radiation header 114. Thus, the semiconductor heating element 110 and the metallic casing 116 can be easily connected with each other without being influenced by the component arrangement and the heat is carried out highly efficiently by driving the liquid. In the radiation header 114, since the radiation header 114 and the metallic casing 116 are thermally connected with each other, the heat is broadly diffused to the metallic casing 116 because of a high thermal conductivity of the metallic casing 116.
However, in the conventional first cooling apparatus, the cooler 103 for performing heat exchange between the heating component 101 and the refrigerant and thus cooling the heating component 101, the radiator 104 for removing the heat from the refrigerant, and the pump 105 for circulating the refrigerant are required. To combine these elements, the apparatus is large-sized and complicated and miniaturization thereof is difficult. That is, the conventional first cooling apparatus is originally suitable for cooling a large electronic equipment, but it cannot cope with a recent portable notebook model personal computer of high performance which is small, light and thin and is to be carried in various postures.
As the electronic equipment become smaller and thinner, a cooling apparatus needs to become smaller in size. Therefore, gasification of the refrigerant and mingling of resulting bubbles, which, although can still be problematic in large-sized equipment, may potentially be ignored in the case of a relatively large-sized equipment, can become more problematic in smaller devices such as a portable lab-top computer. In particular, air bubbles formed in the flow passage of a radiator can accumulate in the pump, resulting in air-lock and deterioration in the pump operation. That is, as gasification of the refrigerant and mingling of bubbles occur, the bubbles begin to accumulate in the piping 106 and the pump 105. If the apparatus is used in this state for a long time, the pump 105 will be inoperable because of air lock due to the growing bubbles and the efficiency of heat exchange will be gradually lowered. It is difficult for the user side to exhaust the air which has already been accumulated. Moreover, such troubles in the cooling apparatus determine the life of the electronic equipment.
Meanwhile, the conventional second cooling apparatus can be used in a notebook model personal computer or the like, but both the separate structures of a flat heat-receiving header 113 mounted on the semiconductor heating element 110 and the radiation header 114 in contact with the wall of the metallic casing 116 have to be box-shaped and thick, preventing reduction in thickness of the notebook model personal computer. Moreover, similarly to the first conventional cooling apparatus, the conventional second cooling apparatus does not have any mechanism by which to remove and restrict air bubbles from the fluid passageway of the radiator. Accordingly, in the conventional cooling apparatus said air bubbles can flow through the pump and accumulate therein. Accordingly, it cannot be avoided that bubbles which entered the flow paths of these headers grow and cause air lock in the pump, and no measures have been taken against this, whereby the prior art has not considered nor attempted to solve such problems. Moreover, the prior art has not considered removal of air bubbles from a cooling flow path, let alone removal of such air bubbles when used with a portable device which can be positioned in various spatial orientations.
Furthermore, though the radiation header 114 in contact with the wall of the metallic casing 116 can be attached to the metallic casing 116 with a thermal compound or a highly thermal-conductive silicon rubber held between them, or can be directly attached to the metallic casing 116 by screwing or the like, the radiation header 114 has poor heat transfer efficiency and its cooling capability is limited. It may be considered to increase the radiation area to enhance the cooling capability, but simply increasing the area also extends the flow path and increase the quantity of circulation and size of the various components, resulting in an increased possibility of air lock and a shorter life while at the same time increasing the size of the apparatus (e.g., box-shaped radiator is made larger, interfering with the spacing within the computer and its circuitry). The increase in quantity of circulation leads to increase in weight, which is counter to the goal of reducing weight, for example, in smaller portable computers. Therefore, for the radiation header 114 of the second cooling apparatus, the increase in radiation area to enhance the thermal conductivity has contradictory effects.
Conventionally, no measures can be taken against air lock. In fact, it has been considered difficult to use a cooling apparatus of this type in an electronic equipment which is used in various postures like a notebook model personal computer. This is because inherent movement of a portable computer into various positions facilitates movement of air bubbles into the flow passageway so as to increase the concentration therein, whereby accumulation of air bubbles in the pump may increase so as to increase the chances of air-lock. Even if this cooling apparatus is employed, the intended small size, light weight and reduced thickness must be sacrificed. As the capability of CPU is improving as in recent years and higher cooling capability is demanded, the conventional first and second cooling apparatuses, which has the above-described problems, cannot satisfactorily cope with the reduction in size, weight and thickness of notebook model personal computers nor prevent air-lock resulting from air bubble formation in the fluid passageway.
Thus, it is an object of the present invention to provide a cooling apparatus for electronic equipment which enables improvement in efficiency of heat exchange and prevention of air lock.
It is another object of the present invention to provide a cooling apparatus for electronic equipment which enables reduction in size, weight and thickness and has a simple structure.
In order to achieve the foregoing objects, in a cooling apparatus for electronic equipment according to the present invention, an internal circulation path constituting a part of a closed circulation path is provided in a radiator, and at least said internal circulation path and a reserve tank are formed by abutment by joining a radiation board on which curved surfaces as flow path walls of the internal circulation path and the reserved tank are integrally formed, with another radiation board.
Further, a cooling apparatus for electronic equipment according to the present invention includes a reserve tank which can hold cooling medium outside of the fluid passageway so as to provide a mechanism by which air bubbles can be removed from the fluid flow.
Thus, the efficiency in heat exchange can be improved and no air lock is generated. Reduction in size, weight and thickness is made possible and a simple structure enables reduction in cost. Further, the present invention can have particular advantages when used with a portable computer by eliminating air bubbles from the flow path even when the device is positioned in various spatial orientations.